Engine Not Running Smoothly? Troubleshooting Guide

Hi.

My neighbor's Audi A4 Avant experienced a sudden loss of power on its way home this evening. It has a current mileage of 475,000 km. I quickly brought it to my garage for a quick diagnosis.

The engine is running rough, sputtering, and emitting black smoke from the exhaust. When the fuel lines are opened while the engine is running, there's a noticeable drop in RPM everywhere, but it's only very slight on cylinder 1.

Then I measured the compression.

Cylinder 1: 29 bar.
Cylinder 2: 32 bar.
Cylinder: 3.33 bar.
Cylinder 4: 33 bar.

The injectors from cylinders 1 and 4 were replaced, but the error pattern remains the same.

The head gasket has been leaking oil to the outside in the front area for some time now, but not excessively.

There is no noticeable increase in pressure within the crankcase.

The question now is whether to open the engine and try to fix it, or to get a used engine instead, or just scrap the car. However, the car itself is still in very good condition.

What do these terms mean in this context: head gasket, piston seizure, crack in the piston...?

Sure, no problem.

The compression values don't indicate a mechanical defect, so I definitely wouldn't remove the cylinder head for now. You've already ruled out the injector, so it seems the fuel injection pump is likely the only remaining source of the problem.

Have you checked the start date of the funding?

The difference in cylinder readings is bothering me a bit, but I'm not sure if it's still within the acceptable range.

I just finished work, but apparently the neighborly love doesn't extend to the point where I have to stay up all night .

How can I narrow down or rule out the fuel injection pump as the cause, while keeping costs low in case the car needs to be scrapped?

VAG specifies the maximum difference as 5 bar, which is standard for all TDIs, so it's within range, although not perfect.

Hi there.

I just measured the compression again on the cold engine:

Cylinder 1: 29 bar.
Cylinder 2: 3.5 bar.
Cylinder 3: 31 bar.
Cylinder 4. 32 bar.

So, if there's a pressure difference of 6 bar between two cylinders, could that be the cause of the problem?

Here's the translation:

"Again, how can I diagnose or rule out VP37 as a cause without incurring any costs?"

I will check the start of funding and the timing belt adjustment later. My fingers are frozen at -2 degrees Celsius in the drafty barn, and it's snowing outside .

Hi there,
Is the planetary gear fixed?
Okay, I would like to start by reading the LLR values, both cold and hot.
The pressure difference isn't ideal, but the 29 bar is perfectly acceptable.
hg
Herbert.

I just read out module MWB 13 using my device with model number 1551.

Cylinder 1: 1.80.

Cylinder 2: -1.88

Cylinder 3: 1.88.

Cylinder 4: -1.81

I'll check the valve timing later; I also had the thought that the crankshaft pulley might have rotated.

It looks like it's coming from pot number 1, either the nozzle, or the pressure relief valve, or the cylinder itself.
Check if the error (LLR value) changes location when you swap nozzle 1 with, for example, nozzle 4.
hg
Herbert.

Timing checked and correct, crankshaft pulley not rotated.

The pressure relief valves on cylinders 1 and 3 were faulty, so I replaced them with working ones from a 1Z VP 37.

Nozzles from cylinders 1 and 4 were swapped, and error code 13 was read.

Cylinder 1: 1.88.

Cylinder 2: -1.85

Cylinder 3: 0.69

Cylinder 4: -0.84

The engine runs the same way. When I open the line to cylinder 1, there's no change in RPM, and it smokes like a 40-ton truck from 30 years ago under full load.

Hi there.

Cause found: Hydraulic lifter on cylinder #1 is shattered.

Now the cylinder will be removed, and if the engine block and piston are in good condition, a refurbished cylinder head will be installed, hopefully to reach 500,000 kilometers.

Thank you for the help. If the compression test hadn't gone well, we would have taken off the valve cover a long time ago.

Best regards, Rüdi.

If only the hydraulic lifter is faulty, I wouldn't remove the cylinder head. The effort involved is enormous. Just replace the hydraulic lifter (and the others as well, since they will likely be worn out too), and you're done.
hg
Herbert.

Hi there.

Unfortunately, the cylinder head and camshaft have already been damaged because the valve lifter was moving around in the bore where it's supposed to sit. It might be possible to fix it, but the head gasket has been leaking for a while now, and the exhaust manifold gaskets need to be replaced anyway, so the cylinder head needs to be removed.

I might try installing a used hydrostatic unit to test if the engine runs smoothly again, and then I'll repeat the compression test. But I'll have more information about that next week. Right now, the weather is too nice to be working on things, and I also have other priorities.

Best regards, Rüdi.

And the engine didn't make any unusual noises?
I'm very familiar with this type of failure, but the engines always sounded very unhealthy. I even have a head from an ALH engine where the entire hydraulic lifter guide was completely destroyed as a result.

It was just running roughly; otherwise, there wasn't much else noticeable.

Update: I checked it again yesterday. I secured the timing belt with zip ties to the pulleys, removed the camshaft, carefully extracted the damaged hydraulic lifters from their seats (which required a hammer and chisel), and then smoothed the seats as much as possible using a Dremel tool.

The camshaft was slightly re-ground, and a broken valve stem was replaced.

"I installed used hydraulic lifters from the spare parts bin, put everything back together, and then came the moment: I started the engine. It rumbled for a few seconds, but then it ran smoothly. I took it for a test drive, and at first, everything was covered in blue smoke, but after a few kilometers, that completely disappeared. The performance is as expected."

Now I can replace the head without worrying, knowing that the base and everything else hasn't been damaged. My neighbor was happy to hear familiar sounds again and has given permission for the repair.

I need to rework my replacement head and order some parts first, then I can continue.

Best regards, Rüdi.

Feedback:

It took a while, as I had other projects going on, but the A4 is running smoothly again.

"Used cylinder head disassembled and cleaned, valves re-lapped, new valve stem seals installed, along with new hydraulic lifters and a new camshaft seal."

The defective cylinder head was removed and all necessary components (turbocharger, injectors, etc.) were disassembled. The parts were cleaned and reattached to the replacement cylinder head with new gaskets, studs, and nuts.

"The engine block was cleaned and it was observed that there was no visible wear on the cylinder walls, even with nearly 500,000 kilometers of use. The cross-hatch pattern from the factory honing is still clearly visible, and there are no scratches or unusual deposits present. Even the intake manifold is almost like new thanks to the AGR valve being closed for many years."

The cylinder head is fitted with the highest-quality head gasket to minimize any potential pressure increases in the combustion chamber that might result from a slight warping of the cylinder head.

Last night at 11 PM, the moment finally arrived: my friend started the engine while I was bleeding the fuel lines. After a brief sputter, the engine immediately ran smoothly, and after the new hydraulic lifters filled up, it was as quiet as it hadn't been in years.

"The coolant was filled and bled, and this morning we took it for a test drive. The car is unrecognizable; it runs incredibly smoothly compared to how it used to, and even the small vibrations from the VTG turbo that were always noticeable are gone."

Over the next two days, I'll be testing it out in my daily routine, and then starting on Monday, the A4 can go back on the train to cover its usual 200 km each day.

In a few weeks, I'll be replacing the Hella/Behr air conditioning compressor, a new timing belt (as a precaution, as the one currently installed still has enough life left for another 45,000 km), and a tensioner element (which had seized) for the ribbed belt. All of this will be done at once with a complete front-end service.

Best regards, Rüdi.

Quote:

Cylinder head with the strongest cylinder head gasket installed to minimize potential pressure increases in the combustion chamber due to the cylinder head resurfacing.

It would not have been necessary, and in cases of significant thickness differences (e.g., from a single hole to a three-hole design), it could also cause side effects such as slightly reduced responsiveness.

Nevertheless: Congratulations!